Sniffing RS485 MODBUS data

[jacikaas]

Hello,

I have installed ventilation system in my apartment with this LCD acting like separate device:

It have 4 wires connected. After researching I found main board uses RS485 MODBUS:

I know there is Arduino RS485 modules, which probably could simulate signals to main board. But main problem is I don't know what messages there are. I tried to look for some suggestions on internet, but had no luck. Could some point me how to read this LCD messages to main board so I could simulate same messages over Arduino?

Thanks!